This invention relates to photographic sheet material handling methods and apparatus for large format cameras and more particularly, it concerns a photographic sheet feeding appliance and method for large format, instant cameras in which the image of a subject to be photographed is viewed for focusing and composition at the back of a translucent viewing glass prior to positioning the photosensitive sheet material in front of the glass for exposure and processing.
As described in a commonly assigned U.S. Pat. No. 4,054,231, entitled "Photographic Apparatus" and issued Oct. 18, 1977 to Vaito K. Eloranta, technology is available for incamera exposure and processing of photographic sheet material having image format areas of several square feet. Cameras employing this technology have been constructed and in use have demonstrated a capability for producing photographic prints of exceptionally high quality in formats as large as 40" by 84". While extremely large format cameras of this type are in the nature of a laboratory room which can be entered by an adult person and operated from within to photograph subjects positioned in the optical field of the camera, formats on the order of 20" by 24" can be accomodated by cameras adequately mobile to be transported and positioned in relation to stationary subjects.
The construction of such large format cameras conventionally entails the provision of a lens and shutter supported by a movable lens board defining a light-tight enclosure with a bellows and camera body. Associated with the camera body is a hinged back capable of supporting separate rolls of negative and positive photographic sheet material used in diffusion transfer photographic processing. As is well known in the art, such processing involves the exposure of negative sheet material and the distribution of a processing fluid between the exposed negative and a superimposed positive sheet to which the latent negative image is transferred as a positive photographic print. As disclosed in the afore-mentioned patent, the negative sheet material in large format cameras of the general type under discussion is preferably fed downwardly in the camera film plane from a roll located near the top of the camera body interior. After exposure, the negative is superimposed with a sheet of positive material fed from a roll located near the bottom of the camera body interior. The superimposed sheets are drawn between the nip of a motor driven processing roller pair so that processing fluid deposited on the sheets in accordance with the disclosure of the afore-mentioned patent is spread fully and uniformly over the image format area. As the two sheets and processing fluid are fed through the processing roller pair, they emerge from the bottom of the camera body and after a suitable imbibition time, are separated to provide the finished positive and the spent negative sheet to be discarded.
Because of the format size of such cameras, image composition and focusing is preferably observed at the back of a frosted or translucent glass usually with the aid of a hood to prevent interference by ambient light. Inasmuch as the negative sheet must be positioned in front of the glass for exposure, such viewing for image composition and focusing is not possible with the negative sheet in place for exposure. This problem has been accounted for in the past by providing the negative and positive sheet material with a sufficiently opaque backing that there is no danger of accidental exposure while the material is wound on the roll. By hinging the back of the camera, a length of the negative sheet may be paid from the supply roll with the camera back open sufficiently so that it may be fed through the exit opening at the bottom of the camera back and then a sufficient length of the negative pulled from the roll so that only unexposed negative sheet material is presented at the film plane of the camera for exposure and after the back has been closed. It will be apparent, however, that this procedure not only involved a substantial waste of the negative sheet material, but also required substantial manipulation of the camera back structure after image composition. The time required for such manipulation is an obvious deficiency in photographing live subjects, for example, where movement of the subject is likely.